Body-coupled communications (BCC) or body-based communication has been proposed as a promising alternative to radio frequency (RF) communication for instance as a basis for body area networks (BANs); An example is the standard by the 802.15.6 Task Group of the Institute of Electrical and Electronics Engineers (IEEE). BCC allows exchange of information between a plurality of devices which are at or in close proximity of a body of a human or an animal. This can be achieved by capacitive or galvanic coupling of low-energy electric fields onto the body surface.
In capacitive body coupled communication (BCC) systems information is transmitted from a transmission device to a receiver device via capacitive coupled signals over the user body. Body coupled communication utilizes an electric field rather than an electromagnetic field to transmit information. Capacitive coupling the signal from a small body-worn tag into your body, it generates a minute yet detectable electric field that extends outwardly a couple of centimeters from the entire surface of your skin.
Body coupled communication (BCC) uses the human body as communication channel. It enables wireless communication over a human body between devices that are in contact with that human body. Signals are conveyed over the body instead of through the air. As such, the communication is confined to an area close to the body in contrast to RF communications, where a much larger area is covered. Therefore, communication is possible between devices situated on, connected to, or placed close to the body. Moreover, since lower frequencies can be applied then is typical in RF-based low range communications, it opens the door to low-cost and low-power implementations of BANs or personal area networks (PANs). Hence, the human body is exploited as a communication channel, so that communication can take place with much lower power consumption than in standard radio systems commonly used for BANs (e.g. ZigBee or Bluetooth systems). Since BCC is usually applied in close proximity to the body, it can be used to realize new and intuitive body-device interfaces based on contact or proximity. This creates possibilities for many applications in the field of identification and security.
BCC can be technically realized by electric fields that are generated by a small body-worn tag, e.g., being integrated to a credit card or another suitable device attached to or worn in close proximity to the body. This tag capacitively or galvanically couples a low-power signal to the body. Sometimes this body-coupled communication is referred to as “near-field intra-body communication”. BCC is a wireless technology that allows electronic devices on and near the human body to exchange digital information through capacitive or galvanic coupling via the human body itself. Information is transmitted by modulating electric fields and either capacitively or galvanically coupling tiny currents onto the body. The body conducts the tiny signal to body mounted receivers. The environment (the air and/or earth ground) provides a return path for the transmitted signal.
FIG. 1 shows an exemplary body communication system structure, where data signals are transmitted via couplers placed near or on the body. These couplers transfer the data signal, either galvanically or capacitively, to the body. In the example of FIG. 1, one coupler or electrode provides ground potential GND and the other coupler or electrode is used for transmitting/receiving a signal S. More specifically, transmission from a transmitter (TX) 100 to a receiver (RX) 200 over a human arm is depicted. Generally, every node can in principle act both as transmitter and receiver, i.e., as a transceiver (TRX), and communication can take place from everywhere on the body.
This capacitive nature of body coupled communication systems make is different from conventional radio communication systems. In the latter systems, the antenna has a real-value resistive impedance of 50, 75 ohms or similar, instead of the very high-ohmic capacitive load of the couplers used in body coupled communication. Solutions that improve communication specifically for BCC have been sought for example in the paper “An Energy-Efficient Body Channel Communication based on Maxwell's Equations Analysis of On-Body Transmission Mechanism”, by Joonsung Bae et al., which discloses a transceiver architecture. The transceiver architecture places an inductor in series with a capacitive coupler.